Controlled hardmask shaping to create tapered slanted fins

ABSTRACT

Embodiments described herein relate to methods forming optical device structures. One embodiment of the method includes exposing a substrate to ions at an ion angle relative to a surface normal of a surface of the substrate to form an initial depth of a plurality of depths. A patterned mask is disposed over the substrate and includes two or more projections defining exposed portions of the substrate or a device layer disposed on the substrate. Each projection has a trailing edge at a bottom surface contacting the device layer, a leading edge at a top surface of each projection, and a height from the top surface to the device layer. Exposing the substrate to ions at the ion angle is repeated to form at least one subsequent depth of the plurality of depths.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent ApplicationSer. No. 62/753,847, filed on Oct. 31, 2018, which is hereinincorporated by reference.

BACKGROUND Field

Embodiments of the present disclosure generally relate to opticaldevices for augmented, virtual, and mixed reality. More specifically,embodiments described herein provide for optical device fabrication withtapered fins.

Description of the Related Art

Virtual reality is generally considered to be a computer generatedsimulated environment in which a user has an apparent physical presence.A virtual reality experience can be generated in 3D and viewed with ahead-mounted display (HMD), such as glasses or other wearable displaydevices that have near-eye display panels as lenses to display a virtualreality environment that replaces an actual environment.

Augmented reality, however, enables an experience in which a user canstill see through the display lenses of the glasses or other HMD deviceto view the surrounding environment, yet also see images of virtualobjects that are generated for display and appear as part of theenvironment. Augmented reality can include any type of input, such asaudio and haptic inputs, as well as virtual images, graphics, and videothat enhances or augments the environment that the user experiences. Asan emerging technology, there are many challenges and design constraintswith augmented reality.

One such challenge is displaying a virtual image overlayed on an ambientenvironment. Optical devices, such as waveguides, are used to assist inoverlaying images. Generated light is propagated through an opticaldevice until the light exits the optical device and is overlayed on theambient environment. Fabricating optical devices can be challenging asoptical devices tend to have non-uniform properties. Accordingly, whatis needed in the art are improved optical devices and methods offabrication.

SUMMARY

In one embodiment, a method is provided. The method includes exposing asubstrate to ions at an ion angle relative to a surface normal of asurface of the substrate to form an initial depth of a plurality ofdepths. A patterned multilayer mask is disposed over the substrate andincludes an initial patterned mask disposed over the substrate with twoor more initial projections defining exposed portions of the substrateor a device layer disposed on the substrate. Each initial projection hasa trailing edge at a bottom surface disposed over the substrate. Atleast one subsequent patterned mask with two or more subsequentprojections is disposed over each initial projection of the initialpatterned mask. Each subsequent projection includes a leading edge at atop surface of each subsequent projection and a height from the topsurface to each initial projection. Exposing the substrate to ions atthe ion angle is repeated to form at least one subsequent depth of theplurality of depths.

In another embodiment, a method is provided. The method includesexposing a substrate to ions at an ion angle relative to a surfacenormal of a surface of the substrate to form an initial depth of aplurality of depths, wherein a patterned mask disposed over thesubstrate and includes two or more projections defining exposed portionsof the substrate or a device layer disposed on the substrate. Eachprojection has a trailing edge at a bottom surface contacting the devicelayer, a leading edge at a top surface of each projection, and a heightfrom the top surface to the device layer. Exposing the substrate to ionsat the ion angle is repeated to form at least one subsequent depth ofthe plurality of depths.

In yet another embodiment, a method is provided. The method includesexposing a device layer disposed over a substrate to ions contacting thedevice layer at an ion angle relative to a surface normal of a surfaceof the substrate to form an initial depth of a plurality of depths. Apatterned multilayer mask is disposed on the device layer and includesan initial patterned mask disposed on the device layer with two or moreinitial projections defining exposed portions of the device layer. Eachinitial projection has a trailing edge at a bottom surface contactingthe device layer. The initial patterned mask includes a first materialwith a first erosion rate. At least one subsequent patterned mask withtwo or more subsequent projections is disposed over each initialprojection of the initial patterned mask. Each subsequent projectionincludes a leading edge at a top surface of each subsequent projectionand a height from the top surface to each initial projection. Exposingthe substrate to ions at the ion angle is repeated to form at least onesubsequent depth of the plurality of depths.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above recited features of the presentdisclosure can be understood in detail, a more particular description ofthe disclosure, briefly summarized above, may be had by reference toembodiments, some of which are illustrated in the appended drawings. Itis to be noted, however, that the appended drawings illustrate onlyexemplary embodiments and are therefore not to be considered limiting ofits scope, and may admit to other equally effective embodiments.

FIG. 1 is a front view of an optical device according to an embodiment.

FIG. 2 is a flow diagram of a method for forming an optical devicestructure according to an embodiment.

FIGS. 3A-3G are schematic, cross-sectional views of an optical devicestructure during a method for forming an optical device structureaccording to an embodiment.

FIG. 4 is a flow diagram of a method for forming an optical devicestructure according to an embodiment.

FIGS. 5A-5G are schematic, cross-sectional views of an optical devicestructure during a method for forming an optical device structureaccording to an embodiment.

To facilitate understanding, identical reference numerals have beenused, where possible, to designate identical elements that are common tothe figures. It is contemplated that elements and features of oneembodiment may be beneficially incorporated in other embodiments withoutfurther recitation.

DETAILED DESCRIPTION

Embodiments described herein relate to methods of forming optical devicestructures with tapered fins. The methods include exposing a substrateto ions contacting the substrate or a device layer disposed on thesubstrate at an ion angle relative to a surface normal of a surface ofthe substrate. The utilization of hardmask shaping, i.e., controlling adistance between a leading edge plane defined by the leading edge of thepatterned mask and a trailing edge plane defined by the trailing edge ofthe patterned mask, increases a linewidth of each fin and the depth ofthe fin, which enables the formation of tapered fins in the substrate ordevice layer of the optical device structures.

FIG. 1 is a front view of an optical device 100. It is to be understoodthat the optical device 100 described below is an exemplary opticaldevice. The optical device 100 includes an input coupling region 102defined by a plurality of fins 108, an optical device region 104, and anoutput coupling region 106 defined by a plurality of fins 110.

The input coupling region 102 receives incident beams of light (avirtual image) having an intensity from a microdisplay. Each fin of theplurality of fins 108 splits the incident beams into a plurality ofmodes, each beam having a mode. Zero-order mode (T0) beams are refractedback or lost in the optical device 100, positive first-order mode (T1)beams undergo total-internal-reflection (TIR) through the optical device100 across the optical device region 104 to the output coupling region106, and negative first-order mode (T−1) beams propagate in the opticaldevice 100 a direction opposite to the T1 beams. The T1 beams undergototal-internal-reflection (TIR) through the optical device 100 until theT1 beams come in contact with the plurality of fins 110 in the outputcoupling region 106. The T1 beams contact a fin of the plurality of fins110 where the T1 beams are split into T0 beams refracted back or lost inthe optical device 100, T1 beams that undergo TIR in the output couplingregion 106 until the T1 beams contact another fin of the plurality offins 110, and T−1 beams coupled out of the optical device 100. Oneapproach to control the T1 beams coupled through the optical device 100to the output coupling region 106 and to control the T−1 beams coupledout of the optical device 100 is to control the shape of each fin of theplurality of fins 108 and the plurality of fins 110. A tapered shape foreach fin of the plurality of fins 108 and the plurality of fins 110provides for modulation the field of view and increased opticalbandwidth.

FIG. 2 is a flow diagram of a method 200 for forming an optical devicestructure 300 shown in FIGS. 3A-3G. In one embodiment, the opticaldevice structure 300 corresponds to the input coupling region 102 and/orthe output coupling region 106 of the optical device 100. At operation201, a substrate 302 is exposed to ions 301, such as ion beams. In oneembodiment, which can be combined with other embodiments describedherein, the ions 301 contact the substrate 302 at an ion angle relativeto a surface normal 303 of the surface 304 of the substrate 302. Inanother embodiment, which can be combined with other embodimentsdescribed herein, a device layer 308 is disposed over the substrate 302such that the ions 301 contact the device layer 308 at the ion angle ϑrelative to the surface normal 303 of the surface 304 of the substrate302. In yet another embodiment, which can be combined with otherembodiments described herein, an etch stop layer 306 is disposed betweenthe device layer 308 and the surface 304 of the substrate 302. As shownin FIG. 3F, when the device layer 308 is disposed over the substrate302, the optical device structure 300 includes at least one fin 326formed in the device layer 308. Otherwise, as shown in FIG. 3G, theoptical device structure 300 includes at least one fin 326 formed in thesubstrate 302. While aspects of forming at least one fin 326 in thedevice layer 308 are discussed, it is to be understood that at least onefin 326 in the substrate 302 is similarly formed without the devicelayer 308 disposed thereon.

Exposing one of the substrate 302 to the ions 301 at the ion angle ϑ mayinclude etching processes such as angled ion etching and directionalreactive ion etching (RIE) that accelerate ions 301 to the substrate302. Angled ion etching includes generating an ion beam, such as aribbon beam, a spot beam, or full substrate-size beam, and directing theion beam at the ion angle ϑ to the device layer 308. The ion beam has anetch chemistry corresponding to a gas or gas mixture activated togenerate the ion beam. One example of an angled ion etch system is theVarian VIISta® system available from Applied Materials, Inc. located inSanta Clara, Calif. Directional RIE includes exciting a gas or gasmixture, also known as an etch chemistry, into a plasma by applying aradio frequency (RF) power to the gas or gas mixture and directing ionsof the plasma at the ion angle ϑ to the substrate 302.

In one embodiment, which can be combined with other embodimentsdescribed herein, the device layer 308 includes, but in not limited to,at least one of silicon oxycarbide (SiOC), titanium dioxide (TiO₂),silicon dioxide (SiO₂), vanadium (IV) oxide (VO_(x)), aluminum oxide(Al₂O₃), indium tin oxide (ITO), zinc oxide (ZnO), tantalum pentoxide(Ta₂O₅), silicon nitride (Si₃N₄), titanium nitride (TiN), zirconiumdioxide (ZrO₂), and silicon carbon-nitride (SiCN) containing materials.The substrate 302 includes, but is not limited to, at least one ofamorphous dielectrics, non-amorphous dielectrics, crystallinedielectrics, silicon oxide, polymers, and combinations thereof. In someembodiments, which can be combined with other embodiments describedherein, the substrate 302 includes, but in not limited to, at least oneof an oxide, sulfide, phosphide, telluride, and combinations thereof. Inone example, the substrate 302 includes at least one of silicon (Si),silicon dioxide (SiO₂), sapphire, and high-index transparent materialscontaining materials.

As shown in FIG. 3A, prior to operation 201, a patterned multilayer maskis disposed on one of the device layer 308 and the substrate 302. Thepatterned multilayer mask includes an initial patterned mask 310 and atleast one subsequent patterned mask 312. The initial patterned mask 310is disposed on one of the device layer 308 and the substrate 302. Theinitial patterned mask 310 includes two or more initial projections 311defining exposed portions of the device layer 308 (or the substrate302). The at least one subsequent patterned mask 312 with two or moreprojections 313 is disposed over the initial patterned mask 310. The twoor more projections 313 are substantially aligned with the two or moreprojections 311. Each projection 313 includes a leading edge 315 at atop surface 320 of each projection 313. Each projection 311 has atrailing edge 317 at a bottom surface 318 contacting the device layer308 (or the substrate 302). The initial patterned mask 310 includes apitch 322 between adjacent trailing edges 317. Each projection 311 has afirst height 314 from the bottom surface 318 to the subsequent patternedmask 312. Each projection 313 has a second height 316 from the initialpatterned mask 310 to the top surface 320. Prior to operation 201, thefirst height 314 and the second height 316 are substantially the same.

FIG. 3B is a schematic, cross-sectional view of the substrate 302 atoperation 201. As shown in FIG. 3B, ions 301 contact the device layer308 (or the substrate 302) at the ion angle ϑ relative to a surfacenormal 303 of the surface 304 of the substrate 302. The ions 301 etch aninitial depth 325 of a plurality of depths 327 (shown in FIGS. 3D-3F) ofat least one cavity 368 into the device layer 308 or the substrate 302(FIG. 3G). As shown in FIGS. 3D-3G, each cavity 368 is between twoadjacent fins 326. After operation 201, in addition to the initial depth325, the at least one cavity 368 includes an initial leading sidewallportion 357 of a leading sidewall 359 (shown in FIGS. 3F and 3G), aninitial trailing sidewall portion 361 of a trailing sidewall 364 (shownin FIGS. 3F and 3G), and an initial linewidth 363 from the initialleading sidewall portion 357 to the initial trailing sidewall portion361. The initial leading sidewall portion 357 has an initial leadingangle α_(i) corresponding to the ion angle ϑ relative to the surfacenormal 303. The initial trailing sidewall portion 361 has an initialtrailing angle β_(i) corresponding to the ion angle ϑ relative to thesurface normal 303. The initial linewidth 363 is controlled by adistance 332 between a leading edge plane 334 defined by the leadingedge 315 at a top surface 320 of each projection 313 and a trailing edgeplane 336 defined by the trailing edge 317 at a bottom surface 318contacting the device layer 308 (or the substrate 302). The distance 332corresponds to the initial linewidth 363 as the ions 301 at the ionangle ϑ do not contact the device layer 308 (or the substrate 302)outside of the distance 332. The second height 316 is controlled, i.e.,decreased, such that distance 332 is increased for at least onesubsequent linewidth 365 (shown in FIGS. 3D-3G).

As shown in FIG. 3C, after operation 201, the second height 316 isdecreased. The subsequent patterned mask 312 includes a second materialwith a second erosion rate and the initial patterned mask 310 includes afirst material with a first erosion rate. In one embodiment, which canbe combined with other embodiments described herein, the first materialincludes at least one of TiN, tantalum nitride (TaN), and chromium (Cr)containing materials. In another embodiment, which can be combined withother embodiments described herein, the second material includes atleast one of silicon oxide (SiO_(x)) and SiCN. In yet anotherembodiment, which can be combined with other embodiments describedherein, the second material includes at least one of spin-on-carbon(SOC), photoresist, and bottom anti-reflective coating materials. In oneembodiment, which can be combined with other embodiments describedherein, the second erosion rate is greater than the first erosion ratewhen the device layer 308 is exposed to the ions 301 due to the etchchemistry of the ions 301. For example, the first material contains TiN,the second material contains SiO_(x), and the etch chemistry of the ions301 includes fluoromethane (CH₃F), diatomic oxygen (O₂), and a carriergas, such as argon (Ar). When exposed to ions 301 generated by the etchchemistry of CH₃F, O₂, and Ar, the second material containing SiO_(x)erodes at a greater rate than the first material containing TiN.Therefore, the distance 332 is decreased as the device layer 308 (or thesubstrate 302) is exposed to the ions 301. In another embodiment, whichcan be combined with other embodiments described herein, the seconderosion rate is greater than the first erosion rate dependent of an etchchemistry of an etch process, such as O₂. When exposed to ions generatedby the etch chemistry of O₂, the second material erodes at a greaterrate than the first material. Optional operation 202, includesperforming the etch process to decease the second height 316. In oneembodiment, which can be combined with other embodiments describedherein, the etch process is an isotropic etch process.

At operation 203, operation 201 is repeated to etch at least onesubsequent depth 328 of a plurality of depths 327 of at the least onecavity 368 into the device layer 308 (or the substrate 302). As shown inFIG. 3D, in addition to the subsequent depth 328, the cavity 368includes a subsequent leading sidewall portion 358 of the leadingsidewall 359, a subsequent trailing sidewall portion 362 of the trailingsidewall 364, and a subsequent linewidth 365 from the subsequent leadingsidewall portion 358 to the subsequent trailing sidewall portion 362.The subsequent leading sidewall portion 358 has a subsequent leadingangle α_(s) corresponding to the ion angle ϑ relative to the surfacenormal 303. The subsequent trailing sidewall portion 362 has asubsequent trailing leading angle β_(s) corresponding to the ion angle ϑrelative to the surface normal 303. The subsequent linewidth 365 iscontrolled by the distance 332 between a leading edge plane 334 and atrailing edge plane 336 increased by decreasing the second height 316.The distance 332 corresponds to the subsequent linewidth 365 as the ions301 at the ion angle ϑ do not contact the device layer 308 (or thesubstrate 302) outside of the distance 332. As shown in FIG. 3E,optional operation 204 includes repeating optional operation 202 aftereach subsequent depth 328 of the at least one cavity 368 is etched.

FIG. 3F and FIG. 3G are schematic, cross-sectional views of the opticaldevice structure 300. Operation 201 and optional operation 202 arerepeated until the optical device structure 300 is formed when the leastone cavity 368 has the plurality of depths 327 including the initialdepth 325 and the at least one subsequent depth 328 corresponding to afin depth. The at least one cavity 368 has a critical dimension 366. Thecritical dimension 366 is a full width at half maximum (FWHM) of exposedportions defined by adjacent remaining projections 313 and projections311. Decreasing the initial depth 325 and each subsequent depth 328 willresult in a smoother leading sidewall 359 of the least one cavity 368. Aleading angle α of a plane 376 of the leading sidewall 359 measuredrelative to the surface normal 303 is about 15° to about 70°. A trailingangle β of the trailing sidewall 364 measured relative to the surfacenormal 303 is about 20° to about 75°.

In one embodiment, which can be combined with other embodimentsdescribed herein, the initial patterned mask 310 and the at least onesubsequent patterned mask 312 include non-transparent materials and areremoved after the optical device structure 300 is formed. For example,the initial patterned mask 310 and the at least one subsequent patternedmask 312 include reflective materials, such as Cr or silver (Ag). Inanother embodiment, which can be combined with other embodimentsdescribed herein, the initial patterned mask 310 and the at least onesubsequent patterned mask 312 include transparent materials such thatthe initial patterned mask 310 and the at least one subsequent patternedmask 312 remain after the optical device structure 300 is formed. In oneembodiment, which can be combined with other embodiments describedherein, the etch stop layer 306 is a non-transparent etch stop layerthat is removed after the optical device structure 300 is formed. Inanother embodiment, which can be combined with other embodimentsdescribed herein, the etch stop layer 306 is a transparent etch stoplayer that remains after the optical device structure 300 is formed.

FIG. 4 is a flow diagram of a method 400 for forming an optical devicestructure 500 shown in FIGS. 5A-5G. In one embodiment, which can becombined with other embodiments described herein, the optical devicestructure 500 corresponds to the input coupling region 102 and/or theoutput coupling region 106 of the optical device 100. At operation 401,the substrate 302 is exposed to ions 301. In one embodiment, which canbe combined with other embodiments described herein, the ions 301contact the substrate 302 at an ion angle ϑ relative to a surface normal303 of the surface 304 of the substrate 302. In another embodiment,which can be combined with other embodiments described herein, a devicelayer 308 is disposed over the substrate 302 such that the ions 301contact the device layer 308 at the ion angle ϑ relative to the surfacenormal 303 of the surface 304 of the substrate 302. In one embodiment,the etch stop layer 306 is disposed between the device layer 308 and thesurface 304 of the substrate 302. Exposing the device layer 308 to theions 301 at the ion angle ϑ may include etching processes such as angledion etching and directional RIE that accelerate ions 301 to the devicelayer 308 (or the substrate 302). As shown in FIG. 5F, when the devicelayer 308 is disposed over the substrate 302, the optical devicestructure 500 includes at least one fin 526 formed in the device layer308. Otherwise, as shown in FIG. 5G, the optical device structure 500includes at least one fin 526 formed in the substrate 302. While aspectsof forming at least one fin 526 in the device layer 308 are discussed,it is to be understood that at least one fin 526 in the substrate 302 issimilarly formed without the device layer 308 disposed thereon.

As shown in FIG. 5A, a patterned mask 510 is disposed on the devicelayer 308 (or the substrate 302). The patterned mask 510 includes two ormore projections 511 defining exposed portions of the device layer 308(or the substrate 302). Each projection 511 includes a leading edge 515at a top surface 520 and a trailing edge 517 at a bottom surface 518contacting the device layer 308 (or the substrate 302). The patternedmask 510 includes a pitch 522. The pitch 522 may be measured betweenadjacent trailing edges 517 or adjacent leading edges 515. Eachprojection 511 has a height 514 from the bottom surface 518 to the topsurface 520.

As shown in FIG. 5B, ions 301 contact the device layer 308 (or thesubstrate 302) at the ion angle ϑ relative the surface normal 303 of thesurface 304 of the substrate 302. The ions 301 etch an initial depth 525of a plurality of depths 527 (shown in FIGS. 5D-5G) of at least onecavity 568 into the device layer 308 (or the substrate 302). As shown inFIGS. 5D-5G, each cavity 568 is between two adjacent fins 526. Afteroperation 401, in addition to the initial depth 525, the cavity 568includes an initial leading sidewall portion 557 of a leading sidewall559, an initial trailing sidewall portion 561 of a trailing sidewall364, and an initial linewidth 563 from the initial leading sidewallportion 557 to the initial trailing sidewall portion 561. The initialleading sidewall portion 557 has an initial leading angle α_(i)corresponding to the ion angle ϑ relative to the surface normal 303. Thetrailing sidewall portion 561 has an initial trailing angle β_(i)corresponding to the ion angle ϑ relative to the surface normal 303. Theinitial linewidth 563 is controlled by a distance 532 between a leadingedge plane 534 defined by the leading edge 515 at the top surface 520and a trailing edge plane 536 defined by the trailing edge 517 at thebottom surface 518. The distance 532 corresponds to the initiallinewidth 563 as the ions 301 at the ion angle ϑ do not contact thedevice layer 308 outside of the distance 532. The height 514 and aprojection width 516 of each projection 511 is controlled, i.e.,decreased, such that distance 532 is increased for at least onesubsequent linewidth 365. As shown in FIG. 5C, operation 402 includesperforming an anisotropic etch process to decease the height 514 and theprojection width 516.

As shown in FIGS. 5D-5G, at operation 403, operation 401 and 402 arerepeated to etch at least one subsequent depth 528 of a plurality ofdepths 527 of at the least one cavity 568 into the device layer 308 (orthe substrate 302) until an optical device structure 500 is formed withthe at least one cavity 568 having the plurality of depths 527 includingthe initial depth 325 and the at least one subsequent depth 528corresponding to a fin depth. The cavity 568 includes at least onesubsequent leading sidewall portion 558 of the leading sidewall 559, atleast one subsequent trailing sidewall portion 562 of the trailingsidewall 564, and at least one subsequent linewidth 565 from thesubsequent leading sidewall portion 558 to the subsequent trailingsidewall portion 562. The subsequent leading sidewall portion 558 has asubsequent leading angle α_(s) corresponding to the ion angle ϑ relativeto the surface normal 303. The trailing sidewall portion 561 has asubsequent trailing angle β_(s) corresponding to the ion angle ϑrelative to the surface normal 303. The subsequent linewidth 565 iscontrolled by the distance 532 between the leading edge plane 534 andthe trailing edge plane 536 increasing by decreasing the height 514 andthe projection width 516 via performing the anisotropic etch process.The distance 532 corresponds to the subsequent linewidth 365 as the ions301 at the ion angle ϑ do not contact the device layer 308 (or thesubstrate 302) outside of the distance 532.

As shown in FIG. 5F and FIG. 5G, the at least one cavity 568 has acritical dimension 566. The critical dimension 566 is a FWHM of exposedportions defined by adjacent remaining projections 511. Decreasing theinitial depth 525 and each subsequent depth 528 will result in asmoother leading sidewall 559 and a smoother trailing sidewall 564 ofthe least one cavity 568. A leading angle α of a plane 576 of theleading sidewall 559 measured relative to the surface normal 303 isabout 15° to about 70°. A trailing angle β of a plane 577 of thetrailing sidewall 564 measured relative to the surface normal 303 isabout 20° to about 75°. In one embodiment, which can be combined withother embodiments described herein, the patterned mask 510 includesnon-transparent materials. Therefore, the patterned mask 510 is removedafter the optical device structure 500 is formed. For example, thepatterned mask 510 includes reflective materials, such as Cr or silverAg) In another embodiment, which can be combined with other embodimentsdescribed herein, the patterned mask 510 includes transparent materialssuch that the patterned mask 510 remains after the optical devicestructure 500 is formed. In one embodiment, which can be combined withother embodiments described herein, the etch stop layer 306 is anon-transparent etch stop layer that is removed after the optical devicestructure 500 is formed. In another embodiment, which can be combinedwith other embodiments described herein, the etch stop layer 306 is atransparent etch stop layer that remains after the optical devicestructure 500 is formed.

In summation, methods of forming optical device structures with taperedfins are described herein. The utilization of hardmask shaping, i.e.,controlling a distance between a leading edge plane defined by theleading edge of the patterned mask and a trailing edge plane defined bythe trailing edge of the patterned mask, increases a linewidth of eachfin and the depth of the fin, which enables the formation of taperedfins in a device layer of the optical device structures.

While the foregoing is directed to examples of the present disclosure,other and further examples of the disclosure may be devised withoutdeparting from the basic scope thereof, and the scope thereof isdetermined by the claims that follow.

What is claimed is:
 1. A method comprising: exposing a substrate to ionsat an ion angle relative to a surface normal of a surface of thesubstrate to remove material of the substrate or a device layer disposedon the substrate to form an initial depth of a plurality of depths,wherein a patterned multilayer mask is disposed over the substrate andcomprises: an initial patterned mask disposed over the substrate withtwo or more initial projections defining exposed portions of thesubstrate or the device layer disposed on the substrate, each initialprojection having a trailing edge at a bottom surface disposed over thesubstrate; and at least one subsequent patterned mask with two or moresubsequent projections disposed over each initial projection of theinitial patterned mask, each subsequent projection includes a leadingedge at a top surface of each subsequent projection and a height fromthe top surface to each initial projection; and repeating the exposingthe substrate to ions at the ion angle to remove material of thesubstrate or the device layer to form at least one subsequent depth ofthe plurality of depths in the substrate or the device layer, eachsubsequent depth that is formed has a subsequent linewidth greater thana preceding linewidth of a preceding depth.
 2. The method of claim 1,wherein the initial patterned mask includes a first material with afirst erosion rate and the at least one subsequent patterned maskincludes a second material with a second erosion rate.
 3. The method ofclaim 2, further comprising performing an etch process after theexposing the substrate to ions at the ion angle.
 4. The method of claim3, wherein the second erosion rate is greater than the first erosionrate based on an etch chemistry of the etch process.
 5. The method ofclaim 2, wherein the second erosion rate is greater than the firsterosion rate when the substrate is exposed to the ions.
 6. The method ofclaim 2, wherein each subsequent linewidth is controlled by a distancebetween a leading edge plane of the leading edge and a trailing edgeplane of the trailing edge by decreasing the height.
 7. The method ofclaim 1, wherein the exposing the substrate to ions includes angled ionetching or directional reactive ion etching (RIE).
 8. The method ofclaim 7, wherein angled ion etching includes generating an ion beam anddirecting the ion beam at the ion angle to the substrate.
 9. The methodof claim 1, wherein the initial patterned mask contacts the devicelayer.
 10. A method comprising: exposing a device layer disposed over asubstrate to ions contacting the device layer at an ion angle relativeto a surface normal of a surface of the substrate to remove material ofthe device layer to form an initial depth of a plurality of depths,wherein a patterned multilayer mask is disposed on the device layer andcomprises: an initial patterned mask disposed on the device layer withtwo or more initial projections defining exposed portions of the devicelayer, each initial projection having a trailing edge at a bottomsurface contacting the device layer, the initial patterned mask includesa first material with a first erosion rate; and at least one subsequentpatterned mask with two or more subsequent projections disposed overeach initial projection of the initial patterned mask, each subsequentprojection includes a leading edge at a top surface of each subsequentprojection and a height from the top surface to each initial projection,the at least one subsequent patterned mask includes a second materialwith a second erosion rate greater than the first erosion rate; andrepeating the exposing the device layer to ions contacting the devicelayer at the ion angle to remove material of the device layer to form atleast one subsequent depth of the plurality of depths in the devicelayer, each subsequent depth that is formed has a subsequent linewidthgreater than a preceding linewidth of a preceding depth.
 11. The methodof claim 10, wherein the second erosion rate is greater than the firsterosion rate when the device layer is exposed to the ions.
 12. Themethod of claim 11, further comprising performing an etch process afterthe exposing the device layer to ions the ion angle.
 13. The method ofclaim 12, wherein the second erosion rate is greater than the firsterosion rate based on an etch chemistry of the etch process.
 14. Themethod of claim 10, wherein each subsequent linewidth is controlled by adistance between a leading edge plane of the leading edge and a trailingedge plane of the trailing edge by decreasing the height.